NOTES. xlix 



magnetic mountains of the Oural chain, as well as that of Blago- 

 dat at Kuschwa, Wyssokaja Gora near Nishne Tagilsk, and Katschkanar at 

 Nishne Turinsk, rise out of and have broken through augitic, or rather oura- 

 litic porphyry. In the magnetic mountain of Blagodat, which I visited with 

 Gustave Rose in the Siberian Expedition of 1829, it does not appear that the 

 general action of the parts, which taken separately are found to have magnetic 

 poles, has produced any determinate and recognisable general magnetic axes. 

 Opposite poles lie near each other, irregularly intermingled. The same had pre- 

 viously been found by Erman (Reise um die Erde, Bd. i. S. 362). On the 

 degree of strength of polar force in serpentine, basaltic, and trachytic rocks, com- 

 pared to the quantity of interspersed particles of magnetic iron and oxyde of iron 

 in these rocks, as well as on the influence of atmospheric contact in developing 

 polarity, an influence spoken of earlier by Gme'lin and Gibbs, see the numerous 

 and very estimable observations of Zaddach, in his Beobachtungen iiber die mag- 

 ' netische Polaritat des Basaltes und der trachytischen Gesteine, 1851, S. 56, 65 

 78 and 95. By the comparison, in respect to polarity, of many basaltic frag- 

 ments of columns which had long stood exposed to the atmosphere, and of the 

 sides of other columns for the first time exposed to its contact, and by examining 

 other detached masses, taking away in doing so the earth which covered them, 

 first from their upper and then from their lower portions, Dr. Zaddach thought 

 he could infer (S. 74 and 80) that the polar property, which always appears to 

 be most strong with free access to the atmosphere, and in rock traversed by open 

 fissures, " spreads from the exterior towards the interior, and usually from above 

 downwards." Gme'lin said of the great magnetic mountain, Ulu-utasse-Tau, in 

 the country of the Bashkirs, near the Jaik: " The sides which are exposed to the 

 open air and daylight have the strongest magnetic force; those which are in the 

 earth are much weaker." (Reise durch Sibirien, 1740 1743, Bd. iv. S. 345.) 

 My great teacher, Werner, in his lectures on the Swedish magnetic iron, also 

 expressed his opinion " of the influence of atmospheric contact (not acting by 

 means of increased oxydation) in increasing polarity and attraction." In the mag- 

 netic iron mine of Succassung, in New Jersey, Colonel Gibbs states that " the ore 

 raised from the bottom of the mine has no magnetism at first, but acquires it 

 after it has been some time exposed to the influence of the atmosphere." (On 

 the Connexion of Magnetism and Light, in Silliman's American Journal of 

 Science, vol. i. 1819, p. 89.) Such a statement ought to cause exact experi- 

 ments to be undertaken. In remarking in the text (p. 160) that it is not only the 

 quantity of interspersed particles of iron in a particular kind of rock, but also their 

 relative distribution and arrangement, which affects the strength of the resulting 

 polar force, I considered those particles as so many small magnets. Compare 

 VOL. IV. d 



